Effect of wind speed and relative humidity on atmospheric dust concentrations in semi-arid climates

Abstract

Atmospheric particulate have deleterious impacts on human health. Predicting dust and aerosol emission and transport would be helpful to reduce harmful impacts but, despite numerous studies, prediction of dust events and contaminant transport in dust remains challenging. In this work, we show that relative humidity and wind speed are both determinants in atmospheric dust concentration. Observations of atmospheric dust concentrations in Green Valley, AZ, USA, and Juárez, Chihuahua, México, show that PM10 concentrations are not directly correlated with wind speed or relative humidity separately. However, selecting the data for high wind speeds (>4m/s at 10 m elevation), a definite trend is observed between dust concentration and relative humidity: dust concentration increases with relative humidity, reaching a maximum around 25% and it subsequently decreases with relative humidity. Models for dust storm forecasting may be improved by utilizing atmospheric humidity and wind speed as main drivers for dust generation and transport.

Keywords: Dust emission; PM(10); Relative humidity; Semi-arid; Wind speed.

Figure 1

Field locations for dust monitoring in Green Valley, AZ, USA. Pecan North and Pecan South are located on the edge of a pecan tree grove and beside a dry river bed; Wastewater is located beside the same river bed; PDEQ represents an urban sample; 10 Mile is approximately 10 miles (16 km) from mining activities; HQ (Santa Rita Experimental Range) represents a natural background site chosen for the region. Annual data were taken from Green Valley Fire. Mining activities for the region are labeled in blue.

Figure 2

Field locations for monitoring in Juárez, Chihuahua, Mexico. PM₁₀ monitoring was performed at the two locations show: Location A is surrounded by paved roads and Location B is surrounded by unpaved roads.

Figure 3

Overall average of PM_x for the 9 events during March – May 2011 captured from TSP and Dusttrak observations at the Green Valley sites. The inset shows an expanded version of the plot without the TSP data.

Figure 4

Overall average wind rose for the nine sampling events during March – May 2011 at the Green Valley site.

Figure 5

Wind speed, relative humidity and dust concentration for measurements separated into “Calm”, “Windy”, and “Windy Dusty” events, each containing average of three different measurements, for the Green Valley events. Error bars represent standard deviations of repeat measurements of the same sample.

Figure 6

Wind roses for “Calm”, “Windy”, and “Windy Dusty” events, each corresponding to three different measurements.

Figure 7

PM₁₀ vs. relative humidity (WS>4 m/s) at the Green Valley Fire Station for 2011.

Figure 8

PM₁₀ concentration (μg/m³) contours of relative humidity versus wind speed for Green Valley Fire data.

Figure 9

PM₁₀ concentration (μg/m³) contours compared to relative humidity (%) versus and speed (km/h) from a study in Juárez, Chihuahua Mexico. Location A monitored PM₁₀ near paved roads (top) and Location B monitored near unpaved roads (bottom).